1. Field of the Invention
This invention relates to optical mirrors in general and, in particular, to a mirror having the capability of removing heat from the mirror's relecting facesheet.
2. Summary of the Prior Art
Mirrors utilized in optical systems which require a thermally stabilized reflecting surface are known in the art. Frequently mirrors used in applications in which heat may affect the quality of the image reflected from the reflecting surface or which are subject to high heat loads, for example mirrors used as reflectors in laser systems, will utilize a cooled facesheet to remove heat generated at the reflecting surface. The cooling in such mirrors is often accomplished by passing a cooling fluid through channels in the facesheet or spraying a cooling fluid against the back of the facesheet. In either type of mirror construction, the heat is removed by having the fluid absorb the heat from the facesheet. The fluid is then circulated by means of a pump or other means to a heat exchanger or other form of radiator in which the heat can be removed from the cooling fluid and the fluid recirculated to remove additional heat from the mirror's reflecting surface. The circulation of coolant through a mirror structure can result in the introduction of undesirable vibrations or flow noise which will affect the quality of the optical image reflected from the mirror's surface. Frequently, there is a need for a mirror in which the reflecting surface includes some cooling, but which does not require the extent of heat removal to justify the use of a circulating fluid.
U.S. Pat. No. 4,770,521, which issued on Sept. 13, 1988, discloses a cooled mirror substrate isolator in which a portion of the support structure is constructed of a porus isotropic material having transpiration flow paths to provide cooling of the isolator. The foregoing construction prevents heat extracted by the primary heat exchanger in the mirror from flowing into the mirror's substrate, thereby increasing the stability of the mirror's reflecting surface. U.S. Pat. No. 4,657,359, which issued on Apr. 14, 1987, discloses a transporationally-cooled laser mirror in which a substrate used to support the mirror's reflecting surface is manufactured from a porus material to permit a fraction of the coolant circulated through the mirror's facesheet to bleed through the substrate to provide cooling and thermal isolation of the mirror's substrate. Each of the mirrors described in the foregoing patents require active circulation of coolant to effect cooling of the mirror's reflecting surface.